1. Field of the Invention
The present invention relates to a printing unit and a thermal printer.
2. Description of the Related Art
Hitherto, a printing unit of thermal printers is configured to perform printing by heating a printing surface of a recording sheet with heating elements of a thermal head to develop a color on the printing surface while feeding the recording sheet through rotation of a platen roller under a state in which the recording sheet is nipped between the platen roller and the thermal head. The platen roller includes a gear at one end portion of a shaft. The platen roller is rotated through transmission of power of a motor mounted on a frame of the printing unit to the gear of the platen roller via a reduction gear.
A gearbox portion configured to receive the reduction gear and the gear of the platen roller is formed on the frame of the printing unit. An opening is formed in the gearbox portion in consideration of easiness of assembly of the reduction gear, the platen roller, and the like. The opening of the gearbox portion is covered by a gear cover. The gear cover is engaged with the gearbox portion by snap-fitting.
In the related-art printing unit, however, due to deflection of the gear cover that may be caused due to drop impact, loads applied from the platen roller and the like to the gear cover, and the like, the gearbox portion and the gear cover may be disengaged from each other so that the gear cover drops off from the gearbox portion.
In view of the above-mentioned matter, a printing unit capable of preventing drop of a gear cover, and a thermal printer including the printing unit are demanded in this technical field.